Tune up mod_wsgi settings in example configuration

Explicitly set mod-wsgi process-group to ceilometer-api in sample
This gives the process a good name in process listings.

Set number of process and threads to two and ten respectively. This
represents a reasonable setting to achieve moderate levels of
concurrency.

Change-Id: Iada6126cb525d597cc385c2d63e6228ef08d55a7
Merge "Tune up mod_wsgi settings in example configuration"